Fix for st.h with ruby 1.8.6 and ruby 1.9.1
Fix for st.h with ruby 1.8.6 and ruby 1.9.1

sferik/libxml-ruby,increments/libxml-ruby,xml4r/libxml-ruby,sferik/libxml-ruby,xml4r/libxml-ruby,increments/libxml-ruby,xml4r/libxml-ruby,sferik/libxml-ruby,increments/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby